01 - Bring a large pot of generously salted water to a rolling boil. Add the mafaldine and cook according to package directions, subtracting 2 minutes from the recommended time so the pasta finishes al dente.
02 - Three minutes before the pasta is finished, add the broccoli florets directly to the boiling pasta water. Reserve 1/2 cup of the starchy cooking water, then drain the pasta and broccoli together in a colander.
03 - While the pasta cooks, warm the olive oil in a large skillet over medium heat. Add the sliced garlic and chili flakes if using, and sauté for 1 to 2 minutes until fragrant and just beginning to soften, taking care not to let the garlic brown.
04 - Transfer the drained mafaldine and broccoli to the skillet. Pour in the lemon juice and scatter the zest over the top, along with a splash of the reserved pasta water. Toss vigorously to coat everything evenly, adding more cooking water as needed to build a silky, light sauce.
05 - Sprinkle the grated Parmesan over the pasta and toss until the cheese melts into the sauce and clings to the ribbons of mafaldine. Season with salt and freshly ground black pepper to taste.
06 - Divide among warm plates or bowls immediately. Top with additional Parmesan and a scattering of fresh basil or parsley if desired, and serve right away.